This application claims the priority of 196 33 167.6, filed in Germany on Aug. 17, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an injection nozzle for piston cooling in an internal combustion engine with at least one exit channel to produce a solid/coherent cooling stream.
In internal combustion engines the pistons are under high stress and must frequently be cooled to avoid excessively high piston temperatures. Excessively high piston temperature, especially in alloys, has a negative effect on the long term strength of the piston. In addition, as a result of very high piston temperatures, thermally produced buildup of carbon and deposits in the piston ring grooves may occur. In addition, as the piston temperature increases, because of thermal expansion, deviations from the original piston geometry increase as well. The areas of maximum temperature on the piston bottom depend on the position of the spark plugs, the valve geometry, and the ignition point. The area of maximum temperature is usually located in the vicinity of the exhaust valves.
An effective and relatively economical solution for reducing the piston bottom temperatures is spraying the piston bottom with lubricating oil from the oil circuit of the internal combustion engine. For this purpose, injection nozzles are located in the vicinity of the crankcase and/or the crankshaft drive. The nozzles are connected with the lubricating oil circuit of the engine and an oil stream is directed at the underside of the piston bottom. An injection nozzle of this kind is described, for example, in German Patent Document DE 40 12 475 C2. In such nozzles for producing a solid stream, it has been shown that as the oil temperature increases and the viscosity of the oil begins to fall as oil pressures increase at the same time, the oil stream separates so that a coherent stream of oil no longer reaches the bottom of the piston.
In addition, a spray nozzle for cooling the pistons of an internal combustion engine is known from German Patent Document DE 31 25 835 C2 in which the end channel is formed by folding a tube, thereby forming an end channel having a non-circular shape.
An injection nozzle is known from German Patent Document DE 25 05 019 A1, wherein two or more oil streams are produced that strike different areas of the piston bottom.
An object of the invention is to improve an injection nozzle for cooling the pistons of an internal combustion engine so that a directed coherent oil stream impacts on the piston. The coherent oil stream provides effective cooling over the entire operating temperature range of the internal combustion engine and lubricating oil, especially at high lubricating oil temperatures. An injection nozzle of this kind is simple and economical to manufacture and can be exchanged for conventional injection nozzles without structural changes to the engine.
This object is achieved according to the invention by providing a nozzle which has at least two, at least approximately parallel exit channels spaced apart by a distance smaller than twice the diameter of the larger of the exit channels.
By providing at least two at least approximately parallel end channels in the injection nozzle, and having the distance between the nozzles being less than twice the diameter of the larger exit channel, a directed, coherent and reliable impact on the piston bottom is achieved even at high oil temperatures. As a result of the design of the exit channels according to the invention, even with the same total throughput volume as in a conventional injection nozzle, at high oil temperatures and high pressures, laminar flows form within the channel that prevent the oil stream from prematurely separating. It has been observed that by forming two closely adjacent exit channels according to the present invention, a spray pattern can be produced in which a coherent solid stream forms only 10 mm to 30 mm downstream from the nozzle opening. The resultant improvement in piston cooling can be accomplished without any structural changes to the internal combustion engine. In contrast to conventional injection nozzles, only an end piece provided with the exit channels needs to be replaced by an end piece with two or more parallel exit channels. The nozzle support or the nozzle support inserted into the corresponding receiving bore of the internal combustion engine can be shaped exactly as in conventional injection nozzles.
An especially effective and sharp coherence of the oil stream results when the diameter of the exit channels is between approximately 0.8 mm and 1.5 mm.
It has also been found that the coherence of the resultant solid oil stream is especially good and the flow compartmentalization is especially slight when the distance between the exit channels is in the range between 1 and 2 mm.
It is also especially advantageous according to certain preferred embodiments if the diameter of the two or more exit channels is the same. As a result, an especially uniformly shaped solid stream results that can be directed very accurately at the bottom of the piston to be cooled.
An especially favorable flow pattern within the exit channel is obtained and a resultant sharp coherence of the emerging oil stream is achieved if the input area in the exit channel is expanded conically.
An especially simple and economical design of such a spray nozzle is achieved if the nozzle has a nozzle end piece with the exit channels formed therein, and the end piece is inserted into a sleevelike support part. A check valve can then be integrated for example in this carrier type sleeve part.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.